The present invention generally relates to a link rod of a wiper for a motor vehicle and its manufacturing method and more particularly, to a link rod and its manufacturing method, which improve corrosion resistance of the link rod and reduce manufacturing processes of the link rod.
In response to recent increase of guaranteed life of motor vehicles, there is a growing demand for improvement of corrosion resistance of the motor vehicles. To this end, a link rod for driving a wiper of a motor vehicle is also subjected to cationic electrodeposition coating in order to improve its corrosion resistance.
A known finished link rod 1 subjected to cationic electrodeposition coating is shown in FIGS. 15 to 17 and is produced as follows. Initially, each of opposite end portions of a tubular member is crushed over a predetermined distance by stamping and then, is subjected to punching. Thus, a rod having a predetermined length is obtained in which flat sections 1A and 1B are provided at opposite ends of a cylindrical section 2. Subsequently, a large-diameter hole 4A and a small-diameter hole 5A are, respectively, formed at outer and inner portions of the flat section 1A by punching, while a large-diameter hole 4B and a small-diameter hole 5B are, respectively, likewise formed at outer and inner portions of the flat section 1B by punching. Thereafter, the rod is washed by using cleaning fluid and then, is subjected to cationic electrodeposition coating. Subsequently, the flat sections 1A and 1B are inserted into molds and resinous coupling joints 6A and 6B are molded integrally with the opposite ends of the link rod 1, respectively.
In the above described manufacturing processes of the known link rod 1, the opposite end portions of the tubular member are crushed by stamping so as to be sealed. Nevertheless, as shown in FIG. 17, a minute gap t1 is actually present between an upper plate portion 7A and a lower plate portion 7B. As a result, the cleaning fluid, the coating fluid, hot water, etc. penetrate into the cylindrical section 2 from the gap t1 during the washing process and the coating process. If the cleaning fluid or the coating fluid penetrates into the link rod 1, such problems arise that the cleaning fluid oozing out of the link rod 1 is mixed with the coating fluid so as to not only degrade finishing of the coated surface of the link rod but expedite deterioration of the coating fluid.
In order to eliminate such an inconvenience as described above, fluid drains 8A and 8B are, respectively, formed at opposite end portions of the cylindrical section 2 adjecent to the flat sections 11A and 11B such that the washing fluid penetrating into the cylindrical section 2 is discharged from the fluid drains 8A and 8B.
However, if the link rod 1 is mounted on the motor vehicle without covering the fluid drains 8A and 8B, air, salt water, etc. flow into the link rod 1 from the fluid drains 8A and 8B, thereby resulting in corrosion of the inner surface of the cylindrical section 2. Therefore, at the final manufacturing process of the link rod 1, putty is filled in the fluid drains 8A and 8B so as to form putty plugs 9A and 9B such that the fluid drains 8A and 8B are closed by the putty plugs 9A and 9B, respectively.
Therefore, if a link rod having excellent corrosion resistance should be obtained in the known manufacturing processes, the process of forming the fluid drains and the process of filling the putty in the fluid drains are required to be performed, thus resulting in increase of the number of the manufacturing processes, poor working efficiency and high manufacturing cost.